Rechargeable batteries, secondary batteries or accumulators are employed as batteries in handheld power tools. In particular, the battery has several rechargeable battery cells, for example, lithium-ion accumulator cells. For purposes of prolonging the service life, it is common practice to employ exhaustive-discharge protection, excess-temperature protection and excess-current protection, for instance, in case the tool is overloaded or blocked.
Conventional overload protection or excess-current protection monitors the current drawn from the battery to check whether a defined or pre-specified limit has been exceeded over a given period of time, in which case the tool is switched off. This pre-specified limit is normally far above the normal or average operating current of the electric tool. If the user of the electric tool releases the switch after an actuation or switch-off procedure and then presses the switch again, the tool can once again be operated for the defined period of time.
Particularly with lithium-ion accumulator cells, however, it is not only the case that brief high currents have a detrimental effect on the service life, but it is also the case that relatively low currents during prolonged discharging cycles can already markedly decrease the service life of the lithium-ion accumulator cells. However, conventional current monitoring is not conducive to the envisaged goal here since after a brief interruption, especially by releasing and once again pressing the switch of the tool, the user can already once again operate the tool for a relatively long period of time in the high current ranges of, for instance, 70 A to 100 A.